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# Over the last 150 years, large stretches of salmon habitat have been e

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Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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11 Jul 2012, 23:56
3
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Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.

Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
1. The primary purpose of the passage is to

(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction

[Reveal] Spoiler:
E

2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated

[Reveal] Spoiler:
D

3. According to the passage, human activity has had which of the following effects on salmon populations?

(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction

[Reveal] Spoiler:
B

4. The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to

(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

[Reveal] Spoiler:
C

5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?

(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.

[Reveal] Spoiler:
C

6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

[Reveal] Spoiler:
D

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA
[Reveal] Spoiler: Question #5 OA
[Reveal] Spoiler: Question #6 OA

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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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15 Jul 2012, 22:24
2
KUDOS
OA is EDBC
--------------------------------------------------------------------------------
Q9:
The primary purpose of the passage is to

a. argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
b. correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
c. compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
d. differentiate the particular effects of various human activities on salmon habitats
e. describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction
--------------------------------------------------------------------------------
Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated
--------------------------------------------------------------------------------
Q11:
According to the passage, human activity has had which of the following effects on salmon populations?

a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
--------------------------------------------------------------------------------
Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

Please discuss the options. Questions 10 ~ 12, I found them very difficult and got 3 out of 4l wrong.

OA

EDBC[/quote]
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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19 Jul 2012, 22:53
think for 11 the choice is E because the effect of human activity is not only" numerical one" as line 10 tells habitat loss have had effects on genetic diversity.in line 70 it has been stated that natural disaster and human activity have the same effect on the solmon population.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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26 Jul 2012, 06:38
1
KUDOS
Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated

As given in line 20 “Although some rivers have been recolonized, the unique genes of the original populations have been lost.” This refers that some streams have been initially “DE SALMONed” i.e Salmons fail to return to their natal streams in order to spawn because of some environmental degradation of the stream but somehow the stream was restored and finally recolonized. That’s exactly what option D says (If the stream recovers, an environmentally degraded stream could be recolonized).

Q11:
According to the passage, human activity has had which of the following effects on salmon populations?

a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction

As given in opening lines “Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones;” This clearly refers that human activity caused decline in number of salmons in some river (B)

Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

As given in last para “Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption”, author is clearly comparing the effect of human activity with that of environmental degradation.

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct – Not an example of any process of repopulation
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere – not talking about any particular stream
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured - YES
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams – Clearly out
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance – Clearly out
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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15 Oct 2012, 17:28
Complete discussion is provided at the below mentioned link
over-the-last-150-years-large-stretches-of-salmon-habitat-135658.html#p1103703

Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.

Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.

It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated

[Reveal] Spoiler:
OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?

a) a disturbance of salmonid spawning streams caused by human activtity will increasing the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.

b) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of total spawning population

c) Salmonids in some streams benefit from particular local adaptations

d) Nonenvironmental factors have no effect

e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.

[Reveal] Spoiler:
OA C

Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is To me, the conclusion is that straying because of human effects causes bad things to Salmon in pristine streams. What's the support? Straying causing the dilution of the gene pool. I couldn't find that answer choice.

Thoughts?
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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17 Oct 2012, 07:22
Hey in the first question, we are asked to provide an "inference" which MUST be true according to the passage!
Also, the passage says nothing about dilution during low levels of straying. It just says that with low levels of straying, there is a solid mix of new genes which could be good for the area. That is the are could or could not benefit from low straying. It becomes crucial if the population of fishes decline in the other area which could be increased by moderate level of straying. (please note that the new population could or could not be diluted: not indicated in the passage). It just means that low levels of straying could save a dying fish population.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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17 Oct 2012, 10:17
1
KUDOS
Expert's post
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This post was
BOOKMARKED
voodoochild wrote:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated

[Reveal] Spoiler:
OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.

voodoochild wrote:
The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?
a) a disturbance of salmonid spawning streams caused by human activtity will increasing the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
b) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of total spawning population
c) Salmonids in some streams benefit from particular local adaptations
d) Nonenvironmental factors have no effect
e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.

[Reveal] Spoiler:
OA C

Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is To me, the conclusion is that straying because of human effects causes bad things to Salmon in pristine streams. What's the support? Straying causing the dilution of the gene pool. I couldn't find that answer choice.

You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.

The passage says "high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted." In other words, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. That passage is enormous support for (C)

(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.

Does all this make sense?

Mike
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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18 Oct 2012, 22:21
Mike,

mikemcgarry wrote:
B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.

For the first one, as you have stated above, I think that both of us are on the same page : when the stream gets polluted, the polluted stream's salmon population cannot spawn, and hence they have to find other stream to spawn, leading to straying. Isn't this same as saying "preserving without dilution" i.e. the polluted stream's population can be preserved when there is low-level of straying? Now to extend this idea - why do I think that we can preserve the polluted stream's population? It's because in lines 35-40 it's stated that their genes can be preserved. I am still not able to see why B) is incorrect.

I see dear Douvik's point in that "dilution" is not explicitly stated while discussing 'low levels of straying.' I am not sure whether these are grounds to eliminate B. The passage does talk about high-levels of straying, and has explicitly stated that low-levels of straying is better than high-level straying because of the dilution issue. Can't we infer that the dilution doesn't happen in the case of low-level straying. I am not sure about this. It seems logical to me and within the boundaries of the passage.

mikemcgarry wrote:

(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.

For the second one, this is a great 'assumption' question. Let's dissect this further. Conclusion: "Disturbances cause by humans lower the overall fitness of subsequent generation in 'mixed' streams." Premise, as you stated, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. I agree 100%. That was my understanding as well. However, I am still not able to see the correctness of C).

No let's negate C - Salmonids in none of the streams benefit from particular local adaptations. In my opinion, this has no effect on the conclusion. The conclusion is about comparing the overall fitness levels between "pristine" population (i.e. native population) and "mixed" population (i.e. native + newly strayed ones). Who cares whether 1% of population benefits from the adaptation or 90% of the native population benefits from the adaptation. We are concerned about the causal link between human activity and the lowering of the overall fitness. It could be possible that the native population is only 1% fit, and the straying would decrease this further down to 0.05%. Do I care about the level of fitness of the native population? No. I am only concerned about the "lowering" of fitness. I am still not clear.

Now let's negate E- (I must admit that while solving this question, I was unsatisfied with all the answer choices and had no option than to choose E) from C and E (50% chance ) ) -- I agree that we don't care whether the pristine streams are affected by natural disaster or not. We are only concerned about the link between "human activity" and the lowering of overall Darwinian fitness.

Thanks
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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17 Feb 2013, 08:08
1
KUDOS
Complete discussion is provided at the below mentioned link
over-the-last-150-years-large-stretches-of-salmon-habitat-135658.html#p1103703

GMATPrep wrote:
Over the last 150 years, large stretches of salmon habitat have
been eliminated by human activity: mining, livestock grazing,
timber harvesting, and agriculture as well as recreational and
urban development. The numerical effect is obvious: there are
fewer salmon in degraded regions than in pristine ones; however,
habitat loss also has the potential to reduce genetic diversity. This
is most evident in cases where it results in the extinction of entire
salmon populations. 1ndeed, most analysts believe that some kind
of environmental degradation underlies the demise of many
extinct salmon populations. Although some rivers have been
recolonized
, the unique genes of the original populations have
been lost.

Large-scale disturbances in one locale also have the potential to
alter the genetic structure of populations in neighboring areas,
even ifthose areas have pristine habitats. Why? Although the
homing instinct of salmon to their natal stream is strong, a
fraction of the fish returning from the sea [rarely more than 15
percent] stray and spawn in nearby streams. Low levels of
straying are crucial, since the process provides a source of novel
genes and a mechanism by which a location can be repopulated
should the fish there disappear. Yet high rates of straying can be
problematic because misdirected fish may interbreed with the
existing stock to such a degree that any local adaptations that
are present become diluted. Straying rates remain relatively low
when environmental conditions are stable, but can increase
dramatically when streams suffer severe disturbance. The 1980
volcanic eruption of Mount Saint Helens, for example, sent mud
and debris into several tributaries of the Columbia River. For the
next couple of years, steelhead trout [a species included among
the salmonids] returning from the sea to spawn were forced to
find alternative streams. As a consequence, their rates of straying,
initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as
a result of the disturbances caused by humans, there is no reason
to suspect that the effect would be qualitatively different than
what was seen in the aftermath of the Mount Saint Helens
eruption. Such a dramatic increase in straying from damaged
areas to more pristine streams results in substantial gene ﬂow,
which can in turn lower the overall fitness of subsequent
generations.

According to the passage, human activity has had which of the following effects on salmon population?

1. An increase in salmon population numbers in some previously polluted rivers.

2. A decline in salmon numbers in some rivers.

I answered #1, which is apparently wrong:

GMATPrep wrote:
While human efforts may have been able to clean up some rivers and encourage some salmon to return to them, the passage does not discuss them.

My Argument: Clearly the correct answer has to be about rivers, which are mentioned only once in the passage (highlighted in bold) - and the one mention discusses recolonising or increasing population numbers.

The correct answer is apparently #2:

GMATPrep wrote:
According to the passage, there are fewer salmon in areas that have been degraded by human activity.

My Argument: The question asks about rivers, not areas. The passage mentions regularly the declining population in "areas", "locales" and "habitats" - which are not limited to rivers. The passage does not explicitly discuss reducing populations in rivers.

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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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17 Feb 2013, 08:16
Hi Stormbind,

My advice to you in general would be to look first at the general picture, and see wht that tells you before looking into the minutiae.

It is clear that the overall tone of the first paragraph is that the human influence has been negative. This should guide you in your answer choice.

Whilst you are correct in pointing out that the term 'rivers' is not used in the main passage when referring to human influence, it takes only the smallest bit of common sense to work out that 'habitats' and so forth must mean rivers when talking about salmon.

In answer 1, there is as the passage says no reference to HUMAN inflluence in re-building population. Your highlighted sentence could refer to any number of possible causes for this (global warming changing the temperature of rivers etc)

James
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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17 Feb 2013, 08:28
Hi James,

Thank you for discussing this with me. Sometimes the questions focus on small details, and other times not. I agree that in this example the answer does not consider the small details.

plumber250 wrote:
.. it takes only the smallest bit of common sense to work out that 'habitats' and so forth must mean rivers when talking about salmon.

To the best of my knowledge, habitat refers to an organisms' home or regular residents. A salmon's home is an ocean and not a river. This fact is difficult to ignore because the text discusses extinction, re-population, and straying (an impossible position if salmon did not have habitats beyond their river).

This was of course in the back of my mind while reading the question, and I focused on the details (i.e. river) because the question asks about rivers in a text that is concerned mostly with population change between salmon generations.

Glen
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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07 Jun 2013, 22:28
Good Explanation. Thanks

jaiswalamrita wrote:
Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated

As given in line 20 “Although some rivers have been recolonized, the unique genes of the original populations have been lost.” This refers that some streams have been initially “DE SALMONed” i.e Salmons fail to return to their natal streams in order to spawn because of some environmental degradation of the stream but somehow the stream was restored and finally recolonized. That’s exactly what option D says (If the stream recovers, an environmentally degraded stream could be recolonized).

Q11:
According to the passage, human activity has had which of the following effects on salmon populations?

a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction

As given in opening lines “Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones;” This clearly refers that human activity caused decline in number of salmons in some river (B)

Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

As given in last para “Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption”, author is clearly comparing the effect of human activity with that of environmental degradation.

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct – Not an example of any process of repopulation
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere – not talking about any particular stream
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured - YES
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams – Clearly out
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance – Clearly out
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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25 Sep 2014, 03:51
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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04 Apr 2015, 18:55
On question 12, I think the answer choices boil down to B and C.

Another reason to eliminate B of its wording: "indicate the extent". The first sentence of the third paragraph states "Although no one has quantified changes...there is no reason to suspect that the effect would be qualitatively different...". To me, 'indicate the extent' implies a quantitative answer, which no one has, and so choice C is the best answer.

The rate of straying referred to in the final sentence of the second paragraph is a red herring - pardon the pun.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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27 Jun 2015, 07:58
Good Passage. Completed in 10 mins.
Q4 is tricky, especially during exam conditions.Only POE can save me here.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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20 Aug 2016, 13:43
Is it just me? This passage was extremely hard for me. It took me a very very long time to review the incorrect answers.
Some of the words in the passage and the questions themselves were all difficult.
Also, I felt that this passage required some basic knowledge of fish, which I don't have...

Last edited by tae808 on 20 Aug 2016, 15:13, edited 1 time in total.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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20 Aug 2016, 14:32
Can someone explain "interbreed with existing stock to such a degree that any local adaptations that are present become diluted" means?

So I understand that the passage is saying that high straying rate is problem because they will go to a location where they weren't supposed to go (misdirected) and then, interbreed with the existing stock. What is the "existing stock"? different type of salmon in different area?? (example: white person from America gets lost then ends up in China and interbreed there?) Also, what exactly "local adaptions that are present" mean? Like, the new baby salmons adapt to that environment? or the strayed salmons adapt to that environment?

This is very hard for me... Thanks in advance.
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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20 Aug 2016, 14:33
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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21 Aug 2016, 15:24
tae808 wrote:
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?

Dear tae808,

I'm happy to respond my friend.

A "habitat" is the environment in which a living thing is designed to live, the place where it naturally thrives. For a deer, the habitat is a forest. For a giraffe, the habitat is the Serengeti. For a salmon, the habitat, for at least part of its life cycle, is a stream. Many things live in a healthy stream, so for these animals, it is a habitat. Does this make sense?

Mike
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Re: Over the last 150 years, large stretches of salmon habitat have been e [#permalink]

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21 Aug 2016, 15:39
mikemcgarry wrote:
tae808 wrote:
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?

Dear tae808,

I'm happy to respond my friend.

A "habitat" is the environment in which a living thing is designed to live, the place where it naturally thrives. For a deer, the habitat is a forest. For a giraffe, the habitat is the Serengeti. For a salmon, the habitat, for at least part of its life cycle, is a stream. Many things live in a healthy stream, so for these animals, it is a habitat. Does this make sense?

Mike

I thought salmons are born in the sea and die in the sea. Didn't know that they spend some time in streams.
After reading the passage I thought the streams are mentioned because they move from one point to another...
I really appreciate it!
Re: Over the last 150 years, large stretches of salmon habitat have been e   [#permalink] 21 Aug 2016, 15:39

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